The present invention relates to a charging system of a mobile telephone in which in particular a secondary battery being a power supply of the mobile telephone is charged by connecting with a charger using a car battery as a power source.
FIG. 1 is a block diagram showing the general construction of a mobile telephone. In FIG. 1, a radio wave received at an antenna 301 is amplified at a radio section 302 and the frequency of the radio wave is converted at the radio section 302. The converted signal is demodulated at a modem 303 and further is decoded to a voice signal at a voice processing section 304 and after this the voice signal is reproduced at a speaker 305. On the other hand, a voice inputted from a microphone 306 is transmitted from the antenna 301 processed through the reverse route.
By the operation of an operating section 309, a controller 307 controls a radio channel, the processing of the received data, the voice processing section 304, the display information output of a display 308 and a lighting circuit 310.
The lighting circuit 310 is for example a back light for lighting the display 308 and the operating section 309. The lighting circuit is turned on by a user who operates the operating section 309 in order to make the operation of the mobile telephone possible at the dark place. However, at the case making the lighting circuit 310 always turn on, a battery is consumed, therefore the light is turned on only at the time when the user directs the turning on, and the user is not able to set that the light is always turning on.
However, at the case that the mobile telephone is connected to the charger using a car battery, the secondary battery is charged by the charger using a car battery. Therefore it is possible to make the lighting circuit 310 always turn on by the setting that the user directs the operating section 309 and makes the light always turn on.
As mentioned above, at the case that the mobile telephone is used with the combination of a charger using a car battery, the mobile telephone is usable even at the time during the secondary battery of the mobile telephone is charged by the charger using a car battery. At this case, the user can set to make the light of the display and operating section of the mobile telephone always turn on. However, at the case that the mobile telephone uses a lithium ion battery as a secondary battery, the charging is controlled by a charging current, therefore the current consumed for lighting increases compared with the case that the light of the display and operating section is not turned on, and there is a problem that the charging time becomes long.
It is also possible that the charging current detecting the finish of charging is set to be a large current beforehand by considering the current consumed at the lighting circuit. However, in this case, there is a problem that the charged quantity at the finishing time of charging becomes small in spite of that the charging time does not become longer.
FIG. 2 is a graph showing the characteristic of charging voltage of the secondary battery made of lithium ion. In order to protect the battery, the charging voltage must be controlled to be generally below 4.2 volts. The charging is generally set in the range between 0.1C and 1.5C, in this, C means the nominal capacity of battery. In FIG. 2, the charging of 1C is explained as an example.
The charging current 1C is used for the charging until the charged voltage reaches 4.2 volts. After the charged voltage reached 4.2 volts, the charging current decreases as time passes to make the charged voltage a constant value of 4.2 volts. The charging finishes by detecting the time when the charging current reaches a predetermined value. In this, the predetermined value is set about 0.18C and 92 to 93% of charging capacity.
At the case that the secondary battery being charged supplies the power to the power supply for lighting which is turning on state during the time that the secondary battery is charged, the current consuming at the lighting is added to the charging current. Therefore, at the case to make the charging finish with the predetermined charging current, the time until the charging finish becomes long. Moreover, there is a possibility that the life of the battery will be decreased by charged over the charging capacity being set by considering the battery life and safety.
In order to avoid the above mentioned phenomena, at the case that the charging current of the charging finish is set to a higher value, the charging time does not become longer, however there is a problem that the charged value at the time of the charging finish is lowered.
The Japanese Utility Model Application Laid-Open No. HEI 2-70546 discloses a cordless telephone which provides one master telephone connecting to a telephone line, two handsets connecting to the master telephone by radio communication and a charger. Each handset has a back light and a secondary battery which is charged by the charger. And a current supplying circuit for supplying the current from the charger to the back light of the handset is provided. The charger implements the charging to the secondary battery of the handset and also supplies the current to the back light of the handset during the time that the secondary battery is charged. Therefore, the back light is turning on state during the time that the secondary battery is charged. However, there is no description that the current supply lines are separately provided to the secondary battery and the back light. With this, there is a problem that the charging time will be increased.
The Japanese Patent Application Laid-Open No. HEI 8-64256 discloses a charging method that charges a secondary battery with a predetermined charging current until the charged voltage reaches a predetermined voltage. After the charged voltage reached the predetermined voltage, the charging current is decreased by making the charged voltage a predetermined constant voltage in the time passing. The charging is finished by detecting that the charging curent reaches the predetermined value. However, there is no description that the separate circuit for lighting of the display and operating section is provided during the time that the secondary battery is charged.
It is therefore an object of the present invention to provide a charging system of a mobile telephone at which a secondary battery is not used for the power supply of the lighting of the mobile telephone during the time that the secondary battery is charged.
According to a first aspect of the present invention, for achieving the above mentioned objects, at a charging system of a mobile telephone in which the mobile telephone provides a lighting circuit for lighting a display and an operating section and a secondary battery that is charged by a charger, said mobile telephone provides a power supply terminal for lighting, a change-over switch which connects either said power supply terminal for lighting or a battery connecting terminal to said lighting circuit and a controller which changes said change-over switch to said power supply terminal for lighting by detecting that the mobile telephone is connected to said charger. Said charger provides a charging circuit providing a control means which implements charging with a predetermined charging current until the charged voltage of said secondary battery reaches to a predetermined charged voltage, and makes the charging current decrease with time passing by making the charged voltage a predetermined constant value after the charged voltage reached said predetermined voltage value, and controls to finish charging by detecting that said charging current reached the predetermined value and a power supply for lighting which is provided as a separate line from the said charging circuit and is connected to said power supply terminal for lighting and supplies the current to said lighting circuit during the time that said charging circuit is charging said secondary battery.
According to a second aspect of the present invention, in the first aspect, said charger is a charger using a car battery.
According to a third aspect of the present invention, in the second aspect, said mobile telephone provides a car battery mode detecting terminal and said controller controls said change-over switch by receiving a signal from said car battery mode detecting terminal.
According to a fourth aspect of the present invention, a charger used with the combination of a mobile telephone providing a lighting circuit for lighting a display and an operating section, charges a secondary battery of said mobile telephone provides a charging circuit providing a control means which implements charging with a predetermined charging current until the charged voltage of said secondary battery reaches to a predetermined charged voltage, and makes the charging current decrease with time passing by making the charged voltage a predetermined constant value after the charged voltage reached said predetermined voltage value, and controls to finish charging by detecting that said charging current reached the predetermined value and a power supply for lighting which is provided as a separate line from the said charging circuit and is connected to said power supply terminal for lighting provided at said mobile telephone and supplies the current to said lighting circuit during the time that said charging circuit is charging said secondary battery.
According to a fifth aspect of the present invention, in the fourth aspect, said charger is a charger using a car battery.